The above contributions are obtained under the assumption that perfect CSI is available at the Alice. However, obtaining perfect CSI is ideal, so it is necessary to consider robust security performance of the system.
The authors in [1]}, [2]}, [3]} investigated the robust transmission design in an IRS-aided secrecy system, where the CSI of Eves' channels is not perfectly known. Particularly, a robust secure beamforming problem was formulated to maximize the worst case of SR in [1]}. By replacing the wiretap channels with a weighted combination of discrete samples and then using SDR technique, an efficient AO algorithm was proposed to solve the optimization problem sub-optimally. In [2]}, the authors considered a scenario where two IRSs are deployed to improve the sum SR of multiple single-antenna legitimate receivers in the presence of multiple multi-antenna Eves. Considering the imperfection of the CSI of the Eves' channels, a robust non-convex optimization problem was proposed. Then the design of the transmit covariance, AN covariance matrix and IRS phase shifts was handled by adopting AO, SCA and SDR. In [3]}, the authors first considered the statistical CSI error model and the imperfect cascaded channels of AP-IRS-EVE in IRS-aided secure communications. Then an outage-constrained power minimization problem was formulated. To solve it, the Bernstein-type inequality was exploited to tackle the outage rate probability constraints, and then a sub-optimal algorithm based on AO, the penalty-based and SDR methods were utilized to optimize the variables alternately.
